The present invention relates to power tongs typically used in the oil and gas industry to make up and break apart threaded joints on pipe, casing and similar tubular members. In particular, this invention relates to an improved gear train used within the power tong to prevent undesirable spreading of the power tong""s ring gear.
Power tongs have been in existence for many years and are generally employed in the oil and gas industry to grip and rotate tubular members, such as drill pipe. It is necessary to grip drill pipe with high compressive forces while applying a high degree of torque in order to break apart or tighten threaded pipe connections. In most cases, power tong designs employ a cam mechanism for converting a portion of the torque into a gripping (compressive) force normal to the pipe. This conversion is often accomplished utilizing a power-driven ring gear having an interior cam surface. A cam follower (roller) on a jaw member rides upon the cam surface. As the ring gear is rotated, the follower (and thus the jaw member) is urged into contact with the pipe.
Most current power tong designs include a tong body and ring gear with an open slot or throat, through which the drill pipe is passed in order to place the power tong in position around the pipe. Due to the tremendous forces generated during use, open throat ring gears must resist the tendency to spread during use. Prior art open throat tongs typically employ heavy-duty rollers and other support structure to resist spreading. The prior designs also increase the cross-sectional thickness of the ring gear to help resist spreading. Of course, increasing the cross-section undesirably increases the overall cost and weight of the tong. Despite such attempts to limit spreading, prior art tongs often excessively spread and fail during use, resulting in tremendous costs and down time during expensive drilling operations. Even when there is not out-right operational failure, disproportionate spreading will cause excessive gear tooth wear or other damage which unacceptably reduces the life of the tong.
What is needed in the art is a power tong gear train which will support the throat of a ring gear and limits spreading to an acceptable degree as the throat passes the idler gears. It is desired that any spreading be limited to less than the manufacturing tolerances for which the gears within the tongs are designed.
It is therefore an object of this invention to provide a power tong gear train which prevents spreading of the ring gear to a greater degree than hereto known in the art.
It is another object of this invention to provide an idler gear which incorporates a roller element which supports a bearing surface on the ring gear.
Therefore one embodiment of the present invention provides an improved power tong gear train which includes a ring gear having a series of teeth and a bearing surface. The gear train further includes an idler gear having a series of teeth and a roller element fixed thereto. The idler gear is positioned such that the roller element engages the ring gear""s bearing surface and maintains the tangential orientation of the two gears"" respective pitch diameters.
Another embodiment of the present invention provides an improved idler gear for a power tong gear train. The improved idler gear includes a gear having a pitch diameter and a roller element fixed to the gear. The roller element has a diameter greater than the pitch diameter of the gear.